| 1. |
- Lundgren, Erik, 1988-
(författare)
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Exploring and modeling response process data from PISA : inferences related to motivation and problem-solving
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores and models response process data from large-scale assessments, focusing on test-taking motivation, problem-solving strategies, and questionnaire response validity. It consists of four studies, all using data from PISA (Programme for International Student Assessment) data.Study I processed and clustered log-file data to create a behavioral evaluation of students' effort applied to a PISA problem-solving item, and examined the relationship between students' behavioral effort, self-reported effort, and test performance. Results show that effort invested before leaving the task unsolved was positively related to performance, while effort invested before solving the tasks was not. Low effort before leaving the task unsolved was further related to lower self-reported effort. The findings suggest that test-taking motivation could only be validly measured from efforts exerted before giving up.Study II used response process data to infer students' problem-solving strategies on a PISA problem-solving task, and investigated the efficiency of strategies and their relationship to PISA performance. A text classifier trained on data from a generative computational model was used to retrieve different strategies, reaching a classification accuracy of 0.72, which increased to 0.90 with item design changes. The most efficient strategies used information from the task environment to make plans. Test-takers classified as selecting actions randomly performed worse overall. The study concludes that computational modeling can inform score interpretation and item design.Study III investigated the relationship between motivation to answer the PISA student questionnaire and test performance. Departing from the theory of satisficing in surveys a Bayesian finite mixture model was developed to assess questionnaire-taking motivation. Results showed that overall motivation was high, but decreased toward the end. The questionnaire-taking motivation was positively related to performance, suggesting that it could be a proxy for test-taking motivation, however, reading skills may affect the estimation.Study IV examines the validity of composite scores assessing reading metacognition, using a Bayesian finite mixture model that jointly considers response times and sequential patterns in subitem responses. The results show that, the relatively high levels of satisficing (up to 30%) negatively biased composite scores. The study highlights the importance of considering response time data and subitem response patterns when the validity of scores from the student questionnaire.In conclusion, response process data from international large-scale assessments can provide valuable insights into test-takers’ motivation, problem-solving strategies, and questionnaire validity.
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| 2. |
- Lundgren, Jonas, 1993-, et al.
(författare)
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Flow–heat topology optimization of internally cooled high temperature applications using a voxelization approach for domain initialization
- 2023
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Ingår i: Engineering optimization (Print). - : Taylor & Francis. - 0305-215X .- 1029-0273.
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented for obtaining topology optimized designs for internally cooled high temperature applications, using a flexible geometry description, by means of a voxelization methodology and a novel boundary detection algorithm. A conjugate heat transfer approach is taken; the physics is described by a Stokes-Brinkman model for the flow, weakly coupled with a convection-diffusion model for the heat transfer. A practically relevant optimization formulation, consisting of a maximum temperature objective with a mass flow constraint, is used, and applied to an industrial-relevant non-trivial geometry resembling a guide vane in a gas turbine. Temperatures and velocities from the optimized design are compared with the response from a Stokes flow model with body-fitted mesh and a high-fidelity Reynolds-averaged Navier-Stokes model. A comparison of the performance from a mixed and a penalty approach for solving the flow problem is included. The voxelization approach shows good promise for handling complex design domains.
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| 3. |
- Lundgren, Jonas, 1993-
(författare)
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Internal Cooling Design Using Multiphysics Topology Optimization
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates topology optimization (TO) as a tool for designing optimal internal cooling configurations in components subjected to external hot gas streams. The work is motivated by the challenge of simultaneously considering objectives from multiple physics domains, and the rapid development of additive manufacturing (AM) in the industry, which makes it possible to realize highly complex TO designs. Against this background, a multi-physics TO approach is employed, involving the following physics domains: • Fluid mechanics: describes the flow of the coolant • Heat transfer: describes the coolant and component temperatures • Solid mechanics: describes the structural behaviour of the component Density-based TO is used to parametrize the design, such that the interpolation between solid and fluid material properties is governed by a spatially varying design variable. Temperature measures are considered as objectives in the non-convex optimization problems, and coolant mass flow and structural stiffness measures are considered as constraints. The design process is iterative: for a given design, the flow velocities are computed and used to calculate the temperature distribution, which in turn influences the domain’s structural response. These three equilibrium state problems are solved sequentially, followed by solving corresponding adjoint problems in reversed order, to acquire first-order sensitivity information used by the gradient-based optimization solver. Numerical simulations are carried out for geometries of varying degrees of complexity, resembling gas turbine guide vanes. The simulations cover a range of fidelity levels: from simpler 2D setups to more complex 3D setups with fine resolution, intended for execution on high-performance computing (HPC) clusters. Low-fidelity flow models are utilized in the TO process, while more advanced flow models are employed for design comparisons, and flow and heat response comparisons for given TO designs. The thesis consists of two parts: the first provides the theoretical framework, and the second includes appended papers. In Paper I, only the heat problem is included when modelling convection on internal boundaries identified using the design gradient. Fluid and solid mechanics are introduced in Paper II, where a conjugate heat transfer problem is augmented with a structural model coupled through thermal strains, with numerical examples in 3D. In Paper III, the simultaneous consideration of flow and heat objectives is formulated as a mathematical game between two players trying to minimize the average temperature in the domain and the coolant mass flow through the domain, respectively, with examples in 2D and 3D. The flow problems are the computational bottlenecks, and therefore, Paper IV demonstrates a 3D implementation investigating two different numerical techniques for solving the flow problem, with a voxelization approach for efficient meshing of complex geometries. Paper V presents an efficient, massively parallel HPC implementation for three-field flow-heat-structural models, and addresses further implementation details. This thesis highlights challenging aspects of large-scale multiphysics TO considering fluid mechanics, heat transfer, and solid mechanics.
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| 4. |
- Thore, Carl-Johan, 1981-, et al.
(författare)
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A mathematical game for topology optimization of cooling systems
- 2023
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Ingår i: Zeitschrift für angewandte Mathematik und Mechanik. - : Wiley-V C H Verlag GMBH. - 0044-2267 .- 1521-4001. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- We propose a topology optimization-based method for optimal design of cooling systems in the form of a mathematical game between two players trying to reach a compromise between limiting the amount of a cooling medium used and obtaining low temperatures in the design domain. The flow of the cooling medium is governed by a Stokes-Brinkman flow model with penalty, while the temperature is governed by a stationary convection-diffusion problem whose solution is approximated using a finite element method with consistent stabilization. Existence of solution for the continuum problems and finite element convergence are shown. The idea and performance of the proposed design method are illustrated by numerical examples based on a problem-setting inspired by an industrial design problem for a gas turbine part. The method exhibits good convergence and is able to generate meaningful design concepts representing various levels of compromise between limited use of cooling medium and low temperatures.
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| 5. |
- Thore, Carl-Johan, et al.
(författare)
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Topology optimization for minimum temperature with mass flow and stiffness constraints
- 2022
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier Science SA. - 0045-7825 .- 1879-2138. ; 400
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Tidskriftsartikel (refereegranskat)abstract
- We present a new topology optimization problem formulation for conjugate heat transfer problems based on minimizing temperature subject to mass flow constraints on the flow of a cooling medium and show well-posedness of the continuum problem. A version of the problem augmented with a lower bound on the stiffness of the designs is considered in numerical examples loosely based on a real design case for a gas turbine part. The numerical examples indicate that the proposed problem formulation can be used to obtain designs which are useful from an engineering perspective.
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| 6. |
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| 7. |
- Berglund, Ellinor, et al.
(författare)
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Wellbeing, emotional response and stress among lay responders dispatched to suspected out-of-hospital cardiac arrests
- 2022
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Ingår i: Resuscitation. - : Elsevier Ireland Ltd. - 0300-9572 .- 1873-1570. ; 170, s. 352-360
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Tidskriftsartikel (refereegranskat)abstract
- Background: Systems for smartphone dispatch of lay responders to perform cardio-pulmonary resuscitation (CPR) and bring automated external defibrillators to out-of-hospital cardiac arrests (OHCAs) are advocated by recent international guidelines and emerging worldwide. Objectives: This study aimed to investigate the emotional responses, posttraumatic stress reactions and levels of wellbeing among smartphone-alerted lay responders dispatched to suspected OHCAs. Methods: Lay responders were stratified by level of exposure: unexposed (Exp-0), tried to reach (Exp-1), and reached the suspected OHCA (Exp-2). Participants rated their emotional responses online, at 90 minutes and at 4–6 weeks after an incident. Level of emotional response was measured in two dimensions of core affect: “alertness” – from deactivation to activation, and “pleasantness” – from unpleasant to pleasant. At 4–6 weeks, WHO wellbeing index and level of posttraumatic stress (PTSD) were also rated. Results: Altogether, 915 (28%) unexposed and 1471 (64%) exposed responders completed the survey. Alertness was elevated in the exposed groups: Exp-0: 6.7 vs. Exp-1: 7.3 and Exp-2: 7.5, (p < 0.001) and pleasantness was highest in the unexposed group: 6.5, vs. Exp-1: 6.3, and Exp-2: 6.1, (p < 0.001). Mean scores for PTSD at follow-up was below clinical cut-off, Exp-0: 9.9, Exp-1: 8.9 and Exp-2: 8.8 (p = 0.065). Wellbeing index showed no differences, Exp-0: 78.0, Exp-1: 78.5 and Exp-2: 79.9 (p = 0.596). Conclusion: Smartphone dispatched lay responders rated the experience as high-energy and mainly positive. No harm to the lay responders was seen. The exposed groups had low posttraumatic stress scores and high-level general wellbeing at follow-up. © 2021
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| 8. |
- Berglund, Sara, et al.
(författare)
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Cardiorenal function and survival in in-hospital cardiac arrest : A nationwide study of 22,819 cases
- 2022
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Ingår i: Resuscitation. - : Elsevier BV. - 0300-9572 .- 1873-1570. ; 172, s. 9-16
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Tidskriftsartikel (refereegranskat)abstract
- Background: We studied the association between cardiorenal function and survival, neurological outcome and trends in survival after in-hospital Methods: We included cases aged 18 years in the Swedish Cardiopulmonary Resuscitation Registry during 2008 to 2020. The CKD-EPI equation was used to calculate estimated glomerular filtration rate (eGFR). A history of heart failure was defined according to contemporary guideline criteria. Logistic regression was used to study survival. Neurological outcome was assessed using cerebral performance category (CPC). Results: We studied 22,819 patients with IHCA. The 30-day survival was 19.3%, 16.6%, 22.5%, 28.8%, 39.3%, 44.8% and 38.4% in cases with eGFR < 15, 15-29, 30-44, 45-59, 60-89, 90-130 and 130-150 ml/min/1.73 m2, respectively. All eGFR levels below and above 90 ml/min/1.73 m2 were associated with increased mortality. Probability of survival at 30 days was 62% lower in cases with eGFR < 15 ml/min/1.73 m2, compared with normal kidney function. At every level of eGFR, presence of heart failure increased mortality markedly; patients without heart failure displayed higher mortality only at eGFR below 30 ml/min/1.73 m2. Among survivors with eGFR < 15 ml/min/1.73 m2, good neurological outcome was noted in 87.2%. Survival increased in most groups over time, but most for those with eGFR < 15 ml/min/1.73 m2, and least for those with normal eGFR. Conclusions: All eGFR levels below and above normal range are associated with increased mortality and this association is modified by the presence of heart failure. Neurological outcome is good in the majority of cases, across kidney function levels and survival is increasing.
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| 9. |
- Bergström, Erik, 1976-, et al.
(författare)
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“Check, Check, Check, We Got Those” – Catalogue Use in Information Security Risk Management
- 2023
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Ingår i: Human Aspects of Information Security and Assurance. - Cham : Springer. - 9783031385292 - 9783031385322 - 9783031385308 ; , s. 181-191
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Konferensbidrag (refereegranskat)abstract
- Information Security Risk Management (ISRM) is fundamental in most organisations today. The literature describes ISRM as a complex activity, and one way of addressing this is to enable knowledge reuse in the shape of catalogues. Catalogues in the ISRM domain can contain lists of, e.g. assets, threats and security controls. In this paper, we focus on three aspects of catalogue use. Why we need catalogues, how catalogue granularity is perceived, and how catalogues help novices in practice. As catalogue use is not yet a widespread practice in the ISRM, we have selected a domain where catalogues are a part of the ISRM work. In this case, the Air Traffic Management (ATM) domain uses a methodology that includes catalogues and is built on ISO/IEC 27005. The results are based on data collected from 19 interviews with ATM professionals that are either experts or novices in ISRM. With this paper, we nuance the view on what catalogues can contribute with. For example, consistency, coherency, a starting point and new viewpoints. At the same time, we identify the need to inform about the aim of the catalogues and the limitations that come with catalogue use in order to leverage the use – especially from a novice perspective. © 2023, IFIP International Federation for Information Processing.
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| 10. |
- Bernsmed, Karin, et al.
(författare)
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An evaluation of practitioners’ perceptions of a security risk assessment methodology in air traffic management projects
- 2022
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Ingår i: Journal of Air Transport Management. - : Elsevier. - 0969-6997 .- 1873-2089. ; 102
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Tidskriftsartikel (refereegranskat)abstract
- Cyber security is a key enabler for safe Air Traffic Management (ATM). This paper presents results from an empirical study, in which we have investigated and evaluated the use of the Security Risk Assessment Methodology for SESAR (SecRAM) in European ATM research and development projects. The study was performed with the intention to find and document common issues and aspects that could be improved in the methodology. The results from the study reveal that while most of the practitioners had a positive perception of the methodology itself, they were less satisfied with the process of applying it in their projects. Based on the results, we provide a number of recommendations, which aim to improve the security risk assessment process in the ATM domain.
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